Earth’s long-term climate stabilized by clouds

By Colin Goldblatt, Victoria L. McDonald and Kelly E. McCusker

Abstract

The Sun was dimmer earlier in Earth’s history, but glaciation was rare in the Precambrian: this is the ‘faint young Sun problem’. Most solutions rely on changes to the chemical composition of the atmosphere to compensate via a stronger greenhouse effect, whereas physical feedbacks have received less attention. We perform global climate model experiments, using two versions of the Community Atmosphere Model, in which a reduced solar constant is offset by higher CO2. Model runs corresponding to past climate show a substantial decrease in low clouds and hence planetary albedo compared with present, which contributes 40% of the required forcing to offset the faint Sun. Through time, the climatically important stratocumulus decks have grown in response to a brightening Sun and decreasing greenhouse effect, driven by stronger cloud-top radiative cooling (which drives low cloud formation) and a stronger inversion (which sustains clouds against dry air entrainment from above). We find that systematic changes to low clouds have had a major role in stabilizing climate through Earth’s history, which demonstrates the importance of physical feedbacks on long-term climate stabilization, and a smaller role for geochemical feedbacks.

This article appeared on the Nature Geosciences website at https://ui.adsabs.harvard.edu/abs/2019AGUFM.A11L2768G/abstract